ND Filter Question

[sA x sKy]

Hey everyone, I have a question about ND filters. I'm not sure how many stops I need for what I want to do. I'm looking for the effect where when I do a long exposure of water, the water seems distilled, almost glass looking. Something like this: Brothers. on Flickr - Photo Sharing!.

I was thinking of a 10 stop B+W filter but would that work well for clouds/sunsets as well?

Thanks.

 

[Garbz]

The picture you posted doesn't need an ND filter at all. Just come back at night and use a long exposure then.

Getting water silky smooth requires a few seconds exposure. I'm not sure what you're after with your clouds and sunsets idea. But yeah a 10 stop ND would get a silky water effect.

 

[tirediron]

I think 10 stops might be a bit of overkill and very limiting. I have have two one stop and one three stop NDs in my collection, and have yet to find an occasion when that's not enough. Generally, an ISO reduction, aperture increase and a couple of stops of ND will give you all you need. Depending on the speed at which the water is flowing you will need between 1 and five seconds to get the 'silky' effect.

 

[Dwig]

If you want the effect on a sunny day then you'll need the 10 stop ND. At ISO 200 you'd end up with 4 seconds at f/16 using a 10 stop (1024x filter factor or ND 3.00) filter. At a better aperture for most crop sensor DSLRs you'll be using something more like 1 sec at f/8, which is hardly enough to get a really smooth silky effect.